1. Field of the Invention
The field of art to which this invention relates is solid-state cameras and in particular to solid-state color cameras which supply composite color video signals having interlaced relations between successive two fields.
2. Description of the Prior Art
In the case of using a solid state sensor such as a charge coupled device (hereinafter referred to as a CCD) as an image pickup device for a television camera, input photo or optical informations corresponding to the image of an object are converted to electrical signals in response to sampling at every picture element. So in contrast to well known vidicons, output signals are sampled in a CCD at every picture element. If it is assumed that the sampling frequency is f.sub.c, the alignment pitch .tau..sub.H in the horizontal direction is 1/f.sub.c. The electric charges stored in the respective picture elements are finally transferred to an output terminal at a rate determined by a clock pulse frequency and the video information is derived in serial form. The resultant video signal S.sub.Y contains DC components S.sub.DC and side band components S.sub.SB of the sampling frequency f.sub.c modulated with the DC components S.sub.DC.
The side band component S.sub.SB is distributed upper and lower with respect to the sampling frequency f.sub.c which is at its center. If the frequency band of the DC component S.sub.DC is selected sufficiently wide so as to increase the resolution, a higher band component S.sub.DH of the DC cmponent is superimposed with the side band component and hence a certain part thereof is caused to develop a sampling error. If a picture is reproduced from such a video signal, a flicker is caused in the resulting picture.
Since this flicker is caused by the sampling error, the sampling error and consequently the flicker can be avoided by restricting the frequency band of DC component S.sub.DC to be smaller than one-half of the sampling frequency f.sub.c. However, if the frequency band of the DC component S.sub.DC is restricted as above, the resolution is deteriorated. In order to make the frequency band of the DC component S.sub.DC about 3.5 MH.sub.Z without deteriorating the resolution, the sampling frequency f.sub.c may be made high enough. The sampling frequency f.sub.c is obtained by the product of n.f.sub.H (f.sub.c =n.f.sub.H) where n is the number of picture elements in the horizontal direction of the CCD and f.sub.H is the horizontal frequency of the television signal (practically, an effective scanning time period in the horizontal direction). If the sampling frequency f.sub.c is made so high as to remove the sampling error, the number n of the picture elements must be increased correspondingly, which then results in difficulty in the manufacturing of the CCD.
Further, if such a television camera is provided which handles color signals and produces composite color video signals taking an interlace at every field into account, the number of picture elements in the vertical direction increases and the system design becomes more difficult due to the above mentioned deterioration of signals caused by the signal process at every field.